Grinding machine



United States Patent The invention relates to grinding apparatus particularly for grinding the internal spherically contoured nose surface of radomes.

In manufacturing of ceramic radomes it is important that both the outer and inner surfaces of the radome wall be smoothly contoured and of a closely controlled predetermined dimension throughout to a degree of accuracy that is not readily attainable by the molding method. Such precise dimensional control is necessary to minimize the adverse effect on microwave signals transmitted therethrough. The apparatus disclosed herein is provided for achieving this result on a portion of the inner surface of the radome wall after the other portions of the inner surface have been ground.

It is therefore the primary object of the invention to provide apparatus for precisely grinding the internal spherically shaped nose portion of a radome. Another object of the invention is to provide an apparatus that is light,

simple, sturdy, and compact in construction and economical to manufacture. Another object of the invention is to provide a grinding apparatus for the internal nose portion that may be supported in the proper orientation within the radome. A further object is to provide a grinding apparatus that is self centering upon and maintained on the longitudinal axis of the radome. A still further object is to provide a grinding apparatus that accurately supports and positions the cutting tool. Another object is to provide an apparatus that has a self aligning cutting tool head. Another object is to provide an abrading tool that has the desired contour and line contact with the surface of the work during grinding. A still further object is to provide a grinding apparatus that is counterbalanced and rotatable freely about the axis of the radome.

A radome to be finished by means of this invention is preferably positioned nose down in an external support with its axis disposed vertically.

In the grinding apparatus of the instant invention a circular bearing or ring engages the circular finished in- .ternal surface of the radome adjacent its open end, and

.its lower end supports a universal joint supporting a grinding wheel or cutting tool of a diameter equal to the desired contour and rotatable about an axis perpendicular to the axis of the radome. At the upper end of the shaft is mounted a base supporting a driving motor and a pulley or sheaves engaging a pair of belts extending down along opposite sides of the shaft and around a pair of sheaves respectively adjacent the opposite sides of the grinding wheel for rotating the grinding wheel.

These and other features, objects and advantages of the invention will become apparent in the following description and by the reference to the accompanying drawings in which,

FIG. 1 is a view in elevation partly in section of the apparatus set up for grinding a radome,

FIG. 2 is a sectional view through the apparatus disposed in operative relation to a radome taken approximate- 7 1y on line 22 of FIG. 1,

FIG. 3 is a partial enlarged vertical section through the grinding wheel head, and

FIG. 4 is a view in elevation partly in section of an alternative embodiment of means for supporting the apparatus for grinding a radome.

Referring to the drawings, a workpiece illustrated as a radome R that has had all but the internal spherically contoured nose portion ground is supported within a base 19. The base 18 has a central hole 12, preferably shaped to the contour of the portion of the radome it contacts, through a horizontal supporting member 14 of the base 10. The size of the hole 12 is such that it allows only a small portion of the radome length to pass through and the support '14 is preferably so disposed that the end of the radome at its large diameter is nearly flush with the top of the base 10.

A circular hole 16 in the top of the base 10 is provided concentric with the hole 12 for inserting the radome therethrough and is of a diameter such that its surface closely engages the preground exterior surface of the workpiece comprising radome R.

It should be understood that the embodiment of the base :10 described above and illustrated in the drawing is exemplary only, and that the structural details of the base 1% form no part of this invention. For the satisfactory application of this invention it is sufiicient that the configuration of base 16'- be such that the workpiece such as radome R is rigidly and positively supported in a vertical position and is prevented from being vertically or laterally displaced.

' The grinding apparatus 28 includes a sealed bearing assembly 2Q; interposed between an outer annular supporting member 24 and a centrally disposed inter-supporting member 26. While the bearing assembly '22 may con 'veniently comprise a commercially available unit including separate outer and inner races respectively fixedly secured to the supporting members 24 and 26 in the manner of bearing assembly 52 described below, the showing in FIG. 2 of the drawing has been simplified to the extent that the outer race is shown formed integrally with the relatively enlarged outer supporting member 24 so shaped and positioned that it snugly engages the internal finished surface of the radome R to center the grinding apparatus 29 on the axis of the radome R, and the inner race is shown formed integrally with the inner supporting member 26 provided with a pair of diametrically opposed clearance holes 27 for a pair of drive belts 44 and with an elongated hub or bearing portion 2 8 having a central bore 30 through which a shaft 32 passes and in which the shaft 32 is slidably keyed. The bore 30 through the bearing portion 23 is preferably substantially elongated so that it is effective to maintain the shaft 32 perpendicular to the plane of the bearing assembly :22. In order to avoid an excessive load upon the relatively fragile wall of radome R, the weight of the grinding apparatus 20 is illustrated as supported upon an annular plate '25 con nected by suitable attachment means to the outer supporting member 2'4 and having a peripheral flange for engagement with the upper surface of the base 10. Any suitable attachment means may be used for connecting the outer supporting member 24 to the plate 25 and these attachment means may include a pair of handles or books 29 threadably engaging the plate 25 and the supporting member 24 and useful for lifting the grinding apparatus 20 into and out of engagement with a radome to be ground. In addition, it is preferable that the line along which the outer supporting member -24 engages the inner surface of the radome R be substantially in alignment with the hole 16 in the base 10, as illustrated in the drawing.

Alternatively, the plate 25 can be omitted and all of 3 the weight of the grinding apparatus 26 except that necessary for maintaining axial alignment and to exert the requisite grinding pressure may be supported on a flexible arrangement such as supporting cable connected by means of a suitable bridle to the handles or books 29 and passed through an overhead pulley for connection to a suitable counter-weight.

Such an arrangement is illustrated in FIG. 4.

The shaft 32 has a threaded portion 34 engaged by a feed nut -36 whose bottom surface engages the top surface of the inner supporting member 26 causing the shaft 32 to be displaced vertically in either direction when the nut 36 is rotated.

At the extreme upper end of the shaft 32 is a reduced portion 38 on which is slidably keyed and supported a base or bracket 40 resting against the top surface of a second nut 42 also engaging the threaded portion 34 of the shaft 32.

Fixed to the base or bracket 49 is a motor M and counter-weight C with a handle 41 thereon, by which the grinding apparatus may be rotated. The motor has a pulley 43 fixed to its drive shaft around which is wrapped a pair of drive belts 44 by which the grinding wheel or cutting tool is driven.

While the source of power for motor M is not illustrated, it is to be understood that the motor is connected to a suitable source of electric power through a flexible electrical conduit arranged to permit the necessary displacement of the motor M with the base or bracket 4% upon which it is mounted. In addition, the motor M may be connected to a power source through conventional start and stop switches. The details of these features are not illustrated on the drawing since they are conventional elements which form no part of the instant invention.

In order to further support the shaft 32 and maintain the grinding apparatus precisely coaxial with the radome, a centering device or supporting mechanism St) is provided comprising a bearing 52 having an inner race supporting member 54 which has a central bore 56, closely fitting and slidably engaging the lower end of the shaft 32 by means of a suitable key and keyway. The support ing member 54 is provided with a pair of holes 57 respectively aligned with the holes 27 through which the belts 44 pass. Concentric with the member 54 and fixed rela tive to the outer race of the bearing 52 is a circular sleeve 58. At its lower end the sleeve 58% has a rounded concentric surface 60 engaging the prefinished internal surface of the radome R, preferably at or adjoining the portion thereof supported externally by the surface of the hole 12 in the base 10, in order to minimize the possibility of damaging the radome wall.

In order to further reduce the chance of possible damage to the radome by the centering device 50, a counterbalancing device is provided comprising a pair of extension springs 6-2 having their lower ends hooked around a pair of opposed screws 64 projecting out from the member 54- of the centering device 50, and their upper ends hooked around another pair of opposed screws 66 projecting outwardly from the elongated hub 28. Much but not all of the weight of the centering device 50* is counterbalanced, the springs 62 being of a predetermined sufiicient length and strength so that a substantial part of the weight *of the centering device 50 is relieved and so that the remainder of the weight is sufficient to center the shaft 3-2 of the grinding apparatus 20 and maintain it on the axis of the radome during the grinding operation.

A universally mounted tool head 72 is pivotally attached at the extreme lower end of the shaft 32 in a slot 68 by means of a pin 70 fixed to the shaft 32. The tool head 72 comprises a member 7-4 pivotally supported on the pin 70 and a pivotal tool support 76 pivotally supported :on the member 74 by means of a pin 78 disposed perpendicular to a vertical plane intersecting the axis of pin '70. A cutting tool 84 is rotatably mounted within a slot 80 on a shaft 82 fixedly secured in the tool support 76. The cutting tool 84 is preferably a narrow diamond impregnated peripheral type grinding wheel having a convex cutting surface on its periphery so as to permit line contact with the surface being ground. The cutting tool 84 is of a predetermined diameter which will be that of the finished contour desired within the spherically shaped nose of the radome. To each side of the cutting tool 84', concentric and rotatable therewith, is fastened one of a pair of sheaves or pulleys 86 around which is threaded one of the drive belts 44 through which the cutting tool is rotated by the motor M. The belts 44, threaded through the respective holes 27 and '57 individually, are cut to the desired length and spliced in any suitable manner to form a pair of continuous belts of equal length. The nut 42 is then backed olf or lowered on the threaded portion 34 of the shaft 32 lowering the base 40, motor M and pulley 43. Finally, the belts 44 are wrapped around the pulleys or sheaves 43 and 86, after which the nut 42 is rotated in the other direction, raising the base 40, motor M and pulley 43 to tension the belts 44 properly.

Noting the symmetrical arrangement about the axis of the shaft 32 of the four longitudinally extending strands making up the pair of symmetrically spaced belts 44, it will be apparent that the belts 44 tensioned in the manner described above coact to maintain the universally supported tool head 72 in axial alignment with the shaft 32. However, the provision of the universal mounting for the tool head 72 serves to accommodate initial irregularities in the surface to be ground by the cutting tool 84 by permitting a limited transverse displacement of the cutting tool 84 in response to asymmetrical loads imposed on the cutting tool by such irregularities. However, if the cutting tool 82 is initially displaced from axial alignment with the shaft 32 as it engages the surface to be ground, the continuing tendency of the symmetrically disposed belts 44 to maintain the universally supported tool head 72 and the cutting tool 84 supported thereby in axial alignment with the shaft 32 causes the cutting tool 84 to shift as the grinding operation proceeds until the entire spherically shaped surface formed thereby is concentric with the finished internal surface of the radome.

It can be readily seen from the above description that the grinding apparatus 20 is arranged to be inserted into and removed from a radome easily and that all of its weight is initially supported directly upon the base 10 except for the portion of the weight of the centering device 50 not counter-balanced by the springs 62. Since the radome is required to support only its own weight, the unbalanced weight of the centering device 50, and the slight grinding pressure exerted during the cutting operation with the apparatus 20, the chance of fracturing the relatively fragile wall of the radome is minimized.

It is further apparent that the portion of the grinding apparatus 20 comprising the shaft 32 and the several elements supported thereby may be rotated in the bearings 22 and 52 about a vertical axis coincident with the axis of a radome R in which it is suitably positioned. In the configuration of the instant invention illustrated in the drawing and described above, this rotation is effected by manual displacement of the handle 41 secured to counterweight C in turn secured to the base or bracket 40. Since the cutting tool 84 has only line contact with the surface to be ground, rotation of the grinding apparatus 20 by means of handle 41 through at least is necessary in order to insure that all of the spherically contoured surface at the closed end of the radome is ground by the cutting tool while it is also rotating about a horizontal axis. In actual practice, the grinding apparatus 21 may conveniently be rotated back and forth through a sufficient arc to accomplish this purpose by means of the handle 41.

Finally, it will be apparent that a downward feeding movement of the cutting tool may be had by rotating the feed nut 36 the desired amount allowing the shaft 32 to move downwardly under its own weight.

For operation of the instant invention, a radome R is placed within the base which positively supports it against any further movement. The nut 36 is rotated on shaft 32 so that the cutting tool 84 is withdrawn sufficiently to be sure that it will not contact the surface to be ground before the grinding apparatus is fully seated in the radome R. The grinding apparatus 2% is then lowered into the radome either manually or by other means such as a chain fall or [hoist attached to the hooks or handles 29 provided. During the lowering of the grinding apparatus the centering device 50 first engages the internal surface of the workpiece centralizing the lower end of the shaft 32 and cutting tool 84. Continued lowering of the apparatus allows the shaft 32 to slide within the centering device 59, until the outer race 24 of the bearing 22 centers the apparatus within the radome allowing the flange of plate 25 to rest upon the base 10.

The apparatus is situated in this manner precisely on the axis of the radome with the cutting tool 84 out of contact with the surface to be ground. Motor M is now started by connecting it to a power source not shown and the grinding wheel necessarily rotates at a relatively high speed since it is of a small diameter. The apparatus is now rotated manually by the handle 41 which can also be mechanized if desired. While rotating the apparatus the nut 36 is then rotated relative to shaft 32 to produce a downward feeding movement of the shaft 32 until the cutting tool 84 contacts the surface to be ground. Thereafter, the nut 36 is rotated intermittently in small increments between which adjustments the cutting tool 84 is rotated back and forth about a vertical axis by manipulation of handle 41 so as to overlap the area ground during the preceding rotation, until the workpiece is finished.

Noting that t'm's procedure involves a precision grinding operation, it may be advisable, prior to insertion of grind ing apparatus 29 in a radome, to measure the thickness of the unfinished radome nose portion by any measuring means suitable for this purpose in order to determine the amount of stock that must be removed from the radome wall in the area to be finished by the grinding apparatus 20. This measurement may then serve as a guide to the amount that the cutting tool 84 must be fed downwardly after it initially engages the surface to be ground. In this connection, the actual amount that the cutting tool 84 has been fed may be determined periodically by measuring the distance between a relatively fixed reference such as the top of the stationary plate 25 and the bottom surface of the base or bracket 40 or some other relatively movable portion of the grinding apparatus '29. Notwithstanding such measurements prior to and during the grinding operation, the precise dimensional limitation on wall thickness may necessitate direct measurement of the radome wall thickness at the nose portion thereof periodically during the grinding operation after the grinding apparatus 20 has been removed for this purpose, because the wall thickness before this grinding operation may not be uniform throughout the area to be finished by the apparatus disclosed herein, and hence, may not be an entirely re liable guide to the amount of stock that must be removed.

It is shown by the foregoing description and the accompanying drawings that there has been provided by this invention a simple and practical apparatus for machining the internal spherically contoured nose portion of a radome or the like, of which many modifications may be made by those skilled in the art without departing from the spirit of or scope of the invention as defined in the following claims.

What is claimed is:

1. Apparatus for machining a portion of the inner surface of a radome open at one end and having a circular cross section reduced to the other end to a nose portion with a substantially spherically contoured inner surface, said apparatus comprising a rotatably mounted circular cutting tool convexly shaped transversely of its peripheral surface, spaced coaxial positioning means adapted to engage the internal surface of a radome, means slidable relative to and rotatable within said spaced coaxial positioning means for supporting said cutting tool, means operable to feed said cutting tool toward the spherically contoured inner surface of a radome, and drive means operable to rotate said cutting tool.

2. Apparatus for machining a portion of the inner surface of a radome symmetrical about a central axis and closed at one end thereof by a nose portion with a substantially spherically contoured inner surface, said apparatus comprising a circular cutting tool rotatable about an axis disposed substantially perpendicular to the central axis, spaced coaxial positioning means adapted to engage a portion of the inner surface of a radome previously finished to precise dimensions, supporting means for said cutting tool slidable and rotatable within said spaced coaxial positioning means and disposed thereby on the central axis of a radome, means coacting with said supporting means operable to feed said cutting tool toward the spherically contoured inner surface of a radome, and drive means mounted upon said supporting means operable to rotate said cutting tool about its axis of rotation while said supporting means is rotate about the central axis.

3. Apparatus for machining a portion of the inner surface of an elongated radome closed at one end by a nose portion with a substantially spherically contoured inner surface, said apparatus comprising a cutting tool head, a cutting tool rotatably mounted upon said cutting tool head, longitudinally spaced positioning means adapted to engage the internal surface of a radome, an elongated supporting means for said cutting tool head slidable longitudinally relative to and rotatable centrally of said spaced positioning means so that it may be shifted longitudinally of and rotated Within a radome engaged by said positioning means, means coacting with said elongated supporting means operable to displace said cutting tool longitudinally of a radome, and drive means operable to rotate said cutting tool relative to said cutting tool head about an axis disposed transversely of an elongated radome engaged by said spaced positioning means while said cutting tool head is rotated with said elongated supporting means.

4. Apparatus for machining an internal spherically conoured surface inside of a radome symmetrical about a central axis, said apparatus comprising a circular cutting tool rotatable about a transverse axis disposed in a plane substantially perpendicular to the central axis, spaced coaxial positioning means adapted to engage a portion of the internal surface of a radome previously finished to precise dimensions, supporting means for said cutting tool slidable and rotatable within said spaced coaxial positioning means and disposed thereby on the central axis of a radome, means operable to control movement of said supporting means along the central axis, a universal coupling means inter-connecting said cutting tool and said supporting means, and a cutting tool drive means mounted upon said supporting means and including means to bias said universal coupling means so as to tend to maintain said cutting tool in axial alignment with said supporting means and hence on the central axis of a radome when said cutting tool is rotated about the transverse axis by said drive means while said supporting means is rotated about the central axis.

5. Apparatus for grinding a portion of the inner surface of an elongated radome closed at one end by a nose portion with a substantially spherically contoured inner surface, said apparatus comprising a base arranged to support a radome seated nose down in said base, a bearing assembly including a non-rotatable outer bearing portion and a rotatable inner bearing portion supported thereby, said outer bearing portion including a circumferential shoulder fitted into and adapted to engage the internal surface of a radorne, a supporting flange secured to and supporting said outer bearing portion by engagement with said base, said rotatable inner bearing portion engaging and supported by said outer bearing portion, a vertically disposed shaft rotatable With and slidably keyed to and extending through a central bore in said rotatable inner bearing portion, a centering device a substantial part of the weight of which is counter-balanced slidably mounted on said shaft including a central portion rotatable with said shaft and an annular portion having a shoulder adapted to contact the internal surface of a radorne adjacent the nose thereof, a tool head universally mounted at the lower end of said shaft for rotation with said shaft, a grinding wheel mounted upon said tool head for rotation with said tool head about a diameter of said grinding wheel when said shaft is rotated and for concurrent rotation relative to said tool head about the central axis of said grinding wheel, drive means mounted at the upper end of said shaft connected to and operable to rotate said grinding wheel about its central axis, and means coacting with said shaft operable to feed the grinding wheel axially of said shaft.

6. Apparatus for machining an internal spherically contoured surface inside of a radome, said apparatus comprising a base adapted to engage the external surface of a radome, a bearing assembly'including an outer race and an inner race rotatably supported by the outer race,

the outer race of said bearing assembly-adapted to be disposed in interfitting engagement with the internal surface of a radome to be machined, a supporting flange fixed to said outer race and resting on said base, a shaft rotatable with and slidably keyed to and extending through a central bore in said inner race, a centering device slidably mounted on said shaft movable under predterrnined constraint toward an internal spherically contoured surface inside of a radorne supported in said base including a portion rotatable with said shaft and a peripheral portion adapted to contact the inside of a radorne adjacent an internal spherically contoured surface thereof, a universally mounted tool head attached to one end of said shaft, a cutting tool rotatable on said universally mounted tool head about an axis in a plane substantially perpendicular to the axis of rotation of said shaft, drive means mounted at the other end of said shaft connected to and operable to rotate said cutting tool and means coacting with said shaft operable to feed the cutting tool axially of said shaft.

References Cited in the file of this patent UNITED STATES PATENTS 1,929,888 Hamilton Oct. 10, 1933 2,292,383 Liebmann Aug. 11, 1942 2,824,413 Whitehill Feb. 25, 1958 

1. APPARATUS FOR MACHINING A PORTION OF THE INNER SURFACE OF A RADOME OPEN AT ONE END AND HAVING A CIRCULAR CROSS SECTION REDUCED TO THE OTHER END TO A NOSE PORTION WITH A SUBSTANTIALLY SPHERICALLY CONTOURED INNER SURFACE, SAID APPARATUS COMPRISING A ROTATABLY MOUNTED CIRCULAR CUTTING TOOL CONVEXLY SHAPED TRANSVERSELY OF ITS PERIPHERAL SURFACE, SPACED COAXIAL POSITIONING MEANS ADAPTED TO ENGAGE THE INTERNAL SURFACE OF A RADOME, MEANS SLIDAVLE RELATIVE TO AND ROTATABLE WITHIN SAID SPACED COAXIAL POSITIONING MEANS FOR SUPPORTING SAID CUTTING TOOL, MEANS OPERABLE TO FEED SAID CUTTING TOOL TOWARD THE SPHERICALLY CONTOURED INNER SURFACE OF A RADOME, AND DRIVE MEANS OPERABLE TO ROTATE SAID CUTTING TOOL. 